1. Field
The invention relates to processes for separating selenium and tellurium values from each other, especially such values as they occur in copper anode slimes.
2. State of the Art
Selenium and tellurium are both Group VI B elements and show considerable chemical similarity. They often occur together as impurities in metal sulfide ores. In the electrolytic refining of copper for instance, a slime residue from the impure copper anodes is deposited at the bottom of the electrolytic cells. These anode slimes ordinarily contain significant amounts of selenium and tellurium as well as other values, such as gold and silver.
In the past, various methods have been employed to separate selenium and tellurium from each other. For instance, U.S. Pat. No. 2,039,256 discloses a process in which a copper anode slime is roasted at an elevated temperature in the presence of sulfuric acid. The selenium is volatilized as selenium and selenium dioxide, while the tellurium remains in the slime. Another method used to separate selenium from tellurium in a copper anode slime is disclosed in U.S. Pat. No. 3,419,355. There, sulfur dioxide gas is passed through a filtrate solution obtained by leaching the anode slime with sulfuric acid. Under controlled conditions of temperature and acidity, selenium is precipitated, while the tellurium is left in the solution.
U.S. Pat. No. 4,002,544 discloses the use of concentrated sulfuric acid or oleum to solubilize silver, selenium, tellurium and barium, while sulfating nickel and copper. It is stated that this procedure can be performed in the range of 160.degree.-300.degree. C. but that temperatures below 200.degree. C. are preferred. This patent does not teach the use of concentrated sulfuric acid to effect a separation of selenium and tellurium from each other. Rather, the teaching is to the contrary, i.e. that both selenium and tellurium are dissolved and coexist in the liquid phase solution.